You have your blog set to require registration to post a simple reply.
I often would like to leave a comment about a blog post only to discover that it will require a 5 minute registration drill on my part. Not only that, but I will then have to memorise or record my ID and PW for your system.
If you are a control freak who can't handle public feedback then fine, leave things as they are. But if you want to start a conversation, and are wondering why no one is commenting on your digital pearls of wisdom, now you know.